The present invention relates generally to a mold for producing connecting straps for lead batteries, and in particular, to an improved mold useful in a cast-on-strap (COS) process or the like.
It has long been known, for example from DE-PS No. 1,067,899, that the plate lugs of a group of battery plates of the same polarity can be connected to a corresponding connecting strap by melting lead in a mold having the contours of the connecting strap, including the cell pole, and by dipping the lugs into the melt. This is the so-called cast-on-strap (COS) process, which permits homogeneous connection of the lugs with the connecting straps. After cooling, the connecting strap and the pole are removed from the mold as a one-piece casting. Efficient temperature regulation is extremely important in incorporating these operations into a continuous and efficient production process.
In the manufacture of battery plate groups according to the cast-on-strap (COS) process, a mold designed as a ladle and having a shape which corresponds to the connecting strap and pole to be cast, is first dipped into a melting kettle containing a molten metal, for preheating according to U.S. Pat. No. 2,004,340, for example. The mold is then filled by scooping the appropriate amount of lead from the kettle. The series of battery plates are then dipped into the mold with the plate lugs in an inverted position, whereupon the mold is then intensely chilled by cooling with water. For this purpose, the ladle can be placed into a chilling tank or the like.
In conventional battery constructions, the cross section of the connecting strap tapers in both directions, from the center of the strap longitudinally to its ends. This unequal distribution of material over the length of the strap leads to differences in the rate of heat exchange with the surrounding medium, so that the thinner ends reach the temperature favorable for casting-on of the lugs sooner than the center section, and so that the amount of heat absorbed by the center section of the connecting strap in accordance with the amount of material gathered, tends to accumulate during the cooling phase, causing irregular heat flow.
It is therefore the primary object of the present invention to avoid temperature variations within the molten material during the melting and cooling phases, to the extent possible, during the manufacture of connecting straps and cell poles according to the cast-on-strap (COS) process; in order to create homogeneous casting conditions for the plate lugs at all points along the connecting strap.